He's definitely talented and intelligent but as always people vastly underestimate skill. Humour is a skill that you can learn and he's been doing this comic for ages now. When you've been doing something almost every other day nonstop for years, your brain allocates a ton of cycles to that skill. You start applying that skill all the time, sort of like the Tetris Effect. I bet he gets multiple comic ideas daily reading all sorts of research and memes.